It is well known that the present energy crisis makes desirable achieving practical and efficient techniques for turning solar energy to practical use.
It is recognized in the prior art that solar energy collection panels may desirably incorporate selective absorbers. These selective absorbers have absorptance and emittance which are very different for different wave lengths--high for the sun's shorter wave lengths and low for infrared's longer wave lengths. A curve for one such absorber is shown in FIG. 1. (Reflectance is one minus emittance. Absorptance and emittance are in general the same for any body at a given wave length; in black bodies they are the same at all wave lengths.)
A. B. Meinel and M. P. Meinel, "Applied Solar Energy: An Introduction" (Addison-Wesley, Reading, Mass., 1976), Chapter 9, have described how to obtain a selective absorber by using two layers of material, one to absorb the sunlight and the other to reflect infrared. So too has B. O. Seraphin, "Chemical Vapor Deposition Research for Fabrication of Solar Energy Converter," Tech. Report for NSF-RANN Grant SE/GE-36731, NSF-RA-N-74-128, NTIS Order No. PB-238-947 and NSF-RA-N-75-018, NTIS Order No. PB-241-006; Seraphin taught a layer of sunlight-absorbent silicon deposited by chemical vapor deposition on a reflecting metal surface, and also that a multilayer structure in which successive layers are pure silicon and pure germanium gives nearly ideal selectivity.
Janowiecki et al. U.S. Pat. No. 4,003,770 taught the use of arc plasma spraying to place a layer of silicon on a steel or copper substrate.
It was taught in the prior art (e.g., Goldner and Haskal, "Indium-Tin-Oxide Coated Silicon As a Selective Absorber," Applied Optics, 10, p. 2329 (October, 1975) that a transparent and conductive indium-tin oxide ("ITO") coating reduced infrared radiation from doped and undoped silicon layers. Burk et al., "Fabrication of OSOS Cells by Neutral Ion Beam Sputtering" Proc. of 12th IEEE Photovaltaic Specialists Conference, Baton Rouge, Louisiana (November, 1976), p. 971) taught that when deposited on p-type silicon ITO forms an electrical charge separating barrier which like a suitable pn junction produces an electrical output from a light energy input (i.e., provides a photovaltaic cell).
Green et al. ("Minority Carrier MIS Tunnel Diodes and their Application to Electron and Photo-Voltaic Energy Conversion, Part I: Theory," Solid State Electronics, 17, No. 6, p. 551, June (1974) and Shewchun et al. ("Minority Carrier MIS Tunnel Diodes and their Application to Electron and Photo-Voltaic Energy Conversion, Part II: Experiment," Solid State Electronics, 17, No. 6, p. 563, June (1974)) taught that, when an insulating film thin enough to permit tunnelling of charge carriers is interposed between a semiconductor and a transparent metal coating, useful photovoltaic devices result.
Deposit of semiconductor on aluminum panels by arc plasma spraying to form a pn junction is taught in pending U.S. patent application Ser. No. 724,963, of Henryk Rzewuski, Jurek S. Piekoszewski, and Joseph J. Loferski, "PN Junction Device and Method of Making" now abandoned in favor of pending streamlined continuation Ser. No. 870,562, filed Jan.18, 1978, with which the inventors hereof were familiar before making the invention of the selective absorber panels herein disclosed.